I've been using Sierras in my .264 and worked up max loads. Today, I used the same loads and shot Partitions to find out which loads had the best accuracy to focus on. My most accurate load with the Sierras was the most accurate of all the loads by 1/2". Three of the four shot group were nearly in the same hole at 100 yards. I figured I'd found my load until the bolt was difficult to open on a few. It was definitely hotter than the same load with Sierras.
I only changed the bullet but probably changed the bullet seating depth. I was .012 off the lands with this load but not sure about the depth with Sierras (I know, I should have kept better records).
Anyway, this load is definitely accurate and has the velocity I'd like to keep but the pressures are too much. My guess here is to keep the same load and back off the lands in .003 increments and watch for pressure signs. I backed off the loads in .5 grain increments and accuracy suffered a bit but I'm not sure that it wasn't me getting tired.
I'm guessing I'm either going to have to give up velocity or accuracy here, right? Would just changing the bullet raise pressures pretty dramatically? What's the best way to proceed?
Posts: 249 | Location: Colorado | Registered: 15 March 2002
Yes different bullets can have higher pressure with the same load due to differences in O-Give size and placement, it would be best to start %10 lower than your current load when switching bullets types of the same weight and work your way up till you meet your requirements.
Posts: 593 | Location: My computer. | Registered: 28 November 2001
I'd say start by seating the bullets to recommended depth and work back out toward the lands. Find the actual length to the lands with this bullet, get your distance and your accuracy will be pretty good again, although I doubt as good as the Sierra. It would also be a good idea to back off the powder charge every time you change a component when that close to max. Being careful is way cheaper than an accident due to cutting corners.
As mentioned, changing bullets can change pressures, but, I have found that when substituting NoslerPartiton bullets in place of Sierras, there was usually no unacceptable differences, particularly in accuracy results. My Nosler Partiton loads have mostly been as accurate as ones using Sierras.
The Nosler Partition is longer than the same weight conventional bullet such as the Sierra. Therefore, the effective size of the resistance-free space in which the powder charge begins burning is smaller (volume of the chamber as measured from the base of the bullet when the bullet ogive has fully engaged the lands).
Rules are made to be broken, but you would normally expect the Partition to use a bit less powder for the same pressure. Velocity differences at the same pressure will depend on actual bullet diameter, hardness/slickness, and any number of other factors.
Work up your load for your Noslers without depending too heavily on your experience with the Sierras.
Posts: 13243 | Location: Henly, TX, USA | Registered: 04 April 2001
quote:Work up your load for your Noslers without depending too heavily on your experience with the Sierras.
I'll do that. I'm guessing that if I have to reduce powder to reduce pressures my velocity will go down as well. I've reloaded a few to shoot today using once-fired, neck-sized cases to see if that makes any difference. I wonder if using the neck-sized case that pressure may be reduced since there's more case capacity. I guess I'll see.
Thanks!
Posts: 249 | Location: Colorado | Registered: 15 March 2002
I've found 140 gr Nosler's to produce higher pressure than 140 Sierra's, Hornady's and Speer's in all my 6.5's. If the accuracy is there, Switch to a slower powder and try working up. You may be able to achieve the accuracy and velocity you want that way. Otherwise, back down a couple grains and work your way back up. Using once fired (fire formed) neck sized cases will reduce pressure, but it sounds like you still will need to reduce the load some. I wouldn't expect seating the bullet deeper to reduce the pressure too much. If you keep going deeper, it will eventually raise pressure's again. Anytime there are "signs" of pressure, you can bet you're working at a very high pressure. Good Luck, John
quote:Using once fired (fire formed) neck sized cases will reduce pressure, but it sounds like you still will need to reduce the load some. I wouldn't expect seating the bullet deeper to reduce the pressure too much. If you keep going deeper, it will eventually raise pressure's again.
This is exactly what I figured. Of the six powders I've tried I get the best velocity/accuracty combo with 7828. H870 was accurate but much slower. Maybe I should play with that one again.
Thanks!
Posts: 249 | Location: Colorado | Registered: 15 March 2002
I went to the range and fired some rounds with the bullets seated farther out and also some others with neck-sized only. The pressures went down a touch with the bullets seated farther out. The neck-sized brass left more of an extractor mark but the primers were definitely not as a flat as the same load with full-length resized brass. Accuracy seemed about the same.
Posts: 249 | Location: Colorado | Registered: 15 March 2002
I don't think there's really any difference in pressure between your FL sized and neck sized loads -- a full length sized case will let the primer back out a tad on firing, then will push the head tight against the bolt face when the case stretches under pressure, flattening the primer. The neck-sized case has its head firmly against the bolt face already, so the primer doesn't get a chance to back out and therefore doesn't appear as "flattened". As an example, just look at the case head from a sloppy old lever action .30-30 and see how flat the primers from these mild factory loads appear to be.
With a 140 grain bullet, H 870 should give you higher velocity at the same pressure as 7828. Check both with neck-sized brass, and don't depend so much on the appearance of the primer. Look for other pressure signs such as resistance on opening the bolt, bright head marks, and ultimately, loosened primer pockets.
Posts: 13243 | Location: Henly, TX, USA | Registered: 04 April 2001
That's what I figured about the neck-sized versus full-length sizing regarding headspace.
Everything I've seen in books shows 870 producing about the highest velocities throughout all three of my books but when I ran it through the chronograph it was the lowest by about 100 fps (and a fully compressed load with 75 grains). But, that was only after 40 rounds through the rifle. Now, I've put 150 rounds through it so maybe (hopefully) it's gained a bit after breaking in some. I'm going out later this week with the chrony and a few different powders and loads to see where my velocity ceiling is with each powder.
Posts: 249 | Location: Colorado | Registered: 15 March 2002
